In a healthy human, the integrity of the physiology is such that signals emanating from the heart are well coupled to other parts of the anatomy through the arterial system. Examples are radial pulse signals and heart sounds picked up at the chest.
Existing clinical systems that are used to assess anomalies such as brain trauma, stroke and tumors include computed tomography (CT) scans, magnetic resonance imaging (MRI) and, in the case of brain trauma monitoring, combinations of these with invasive intra ventricular catheters (IVC) or subarachnoid bolts to directly measure intracranial pressure (ICP). There is, however, currently, no way to determine brain disorder without such equipment, leaving decisions on treatment to be delayed in the case of stroke until it can be determined whether the stroke is a bleed or ischemia. In a similar fashion, persons injured at the scene of an accident must be presumed to be brain injured, even if the cause of their non-responsiveness arises from the effects of drugs or alcohol. Another large category of head injuries are those resulting from falls, particularly in the elderly. Immediate assessment of injury would be most helpful while awaiting more comprehensive diagnosis. Non-invasive assessment systems do not exist to determine physiological changes in the brain as a result of injury or disease. This prevents early intervention in the critical time after the brain is first damaged.
Approximately three-quarters of a million individuals suffer from stroke each year in the United States. More than 80 percent of these strokes are caused by occlusion of an artery supplying blood to brain cells (ischemic), the type which might be amenable to therapy with the clot busting medicine, tissue plasminogen activator (TPA). TPA has been shown to significantly reduce disability, but this medication must be given within a short time, typically 3 hours, after stroke symptoms begin. This time window, which tracks damage that begins within minutes after the onset of stroke, is similar to that for trauma patients, and it is known as the “golden window”. TPA treatment is, however, not without risk, because its clot dispersion action raises the potential for intracranial hemorrhage. Due to this side effect it cannot be given to patients who have a stroke caused by bleeding into the brain, termed a hemorrhagic stroke. At the present time, medical treatment awaits the brain CT scan and clinical diagnosis from a skilled team to determine the type of stroke, very often precluding intervention during the precious initial three to six hours. The current system will allow a medic on the scene to differentiate brain ischemia from brain hemorrhage and should significantly increase the percentage of stroke patients who would benefit from TPA and other time-sensitive therapies.
Nearly 2 million people suffer some type of traumatic brain injury each year resulting in 50,000 deaths and high costs to the healthcare system. In order to receive optimum treatment for brain injury, the injury must be diagnosed and treatment begun within one hour after the initial injury. The difficulty is that approximately 50 percent of brain related injuries are drug or alcohol related, generating confusion in the distinction between a person's unresponsiveness as arising from traumatic brain injury (TBI) as distinct from the effects of alcohol or drugs. This lack of diagnostic capability results in the transportation of non-injured patients to trauma centers as well as detracting from the time and effort devoted to the truly injured.
In both stroke and trauma, the current diagnostic capability resides in emergency rooms or trauma centers where there have been tremendous technical advances in brain imaging (MRI and CT scans), flow analysis in cervicocranial arteries, including subtraction angiography, magnetic resonance angiography (MRA), computed tomography angiography (CTA), and extracranial and transcranial Doppler. To date, only the brain CT scan and, in special circumstances, a brain MRI scan can detect changes in brain tissue that indicate either brain ischemia or brain hemorrhage in the case of stroke or various other disturbances to the parenchyma in the case of traumatic brain injury (TBI). Both of these are considered to some extent invasive or intrusive. The use of the non-invasive diagnostic aids, such as continuous wave and pulsed Doppler (Duplex) as well as transcranial Doppler (TCD) have grown as well. Sometimes, a combination of magnetic resonance angiography (MRA) and ultrasound can be useful diagnostic tools for stroke in the hands of a specialist. However, often the accuracy of some of these non-invasive techniques, such as TCD, are technician dependent and these tools are not available to the emergency medical services (EMS) personnel at the scene where transport decisions must be made.
An intracranial pressure (ICP) monitor is disclosed in U.S. Pat. No. 5,919,144, which is incorporated herein by reference. The ICP monitor, which may be used for patients with traumatic brain injury, provides active ensonification of the brain with a known frequency and amplitude of input signal. The change in this signal after transmission through the brain is picked up at a receiving sensor disposed on the outside of the head and the measured change is used to assess brain tissue disturbance.